Information Technology Reference
In-Depth Information
17.7 Exercises
17.8.1
How many pins does a standard D-type parallel port connector have:
(a)
9
(b)
12
(c)
25
(d)
36
17.8.2
What is the maximum transfer rate for ECP/EPP mode:
(a)
100 kB/s
(b)
150 kB/s
(c)
1 MB/s
(d)
1.2 MB/s
17.8.3
Outline the operation of the nibble mode. How does the parallel port allow data to
be inputted?
17.8.4
Design a circuit for nibble mode operation which will sample data bits. The design
should include ground connections (GND), connector types and pin numbers. If
possible, implement the design by adding switches to simulate input levels (power
can be supplied by the parallel port connection).
17.8.5
Explain how several devices can be connected to the parallel port, and identify
how the operating system identifies each of the devices.
17.8 Note from the author
The parallel port was never really been destined for glory. It is basically a legacy port,
which, in the past, was only really useful in connecting printers. The future for printer con-
nections is either with network connections, such as Ethernet, or with a USB connection. In
its standard form, it has a large, bulky connector, which in many systems is never even used.
It has always struggled against the serial port, because it lacks the flexibility of RS-232
and, until recently, had no standards agency to support it. However, it's there and it has
great potential for fast data transfers. RS-232 has always been a great success and has many
of the large manufacturers supporting it, and all importantly, it is defined by several stan-
dards agencies. The key to its current success was due to the intervention of the NPA which
brought together many of the leading computer and printer manufacturers. In these days,
there are only a few major companies, such as Intel and Microsoft, who can lead the market
and define new standards (such as the PCI bus, with Intel).
The main difficulties are how to keep compatibility with previous implementations and
software, and also how to connect multiple devices on a bus system, and allow them to pass
data back and forward without interfering with other devices. This has finally been achieved
with ECP/EPP mode. It is a bit complex, but it works, and even supports data compression.
At the present, my notebook connects to a CD-R drive, a scanner and a printer, all of the
same parallel port (just like SCSI). This arrangement works well most of the time and is a
relative cheap way of connecting devices, but it is in no way as flexible and as fast a SCSI.
